Difference between JOIN and INNER JOIN in Sql Server

Frankly speaking, in Sql Server there is no difference between JOIN and INNER JOIN. They produce the same result and also the same performance.

Let us prove with examples that there is no difference between JOIN and INNER JOIN. Execute the following script to create a demo database with two tables Customers and Orders with sample data as shown in the following image:

joins-demo-tables

CREATE DATABASE SqlHintsJoinDemo
GO
USE SqlHintsJoinDemo
GO
--Create Customers Table and Insert records
CREATE TABLE Customers 
( CustomerId INT, Name VARCHAR(50) )
GO
INSERT INTO Customers
VALUES(1,'Shree'), (2,'Kalpana'), (3,'Basavaraj')
GO
--Create Orders Table and Insert records into it
CREATE TABLE Orders (OrderId INT, CustomerId INT)
GO
INSERT INTO Orders 
VALUES(100,1), (200,4), (300,3)
GO

[ALSO READ] LEFT OUTER JOIN vs RIGHT OUTER

JOIN and INNER JOIN produces the same result

Below table demonstrates that both JOIN and INNER JOIN produces the same result.

JOIN

INNER JOIN

SELECT C.Name 
FROM Customers C 
  JOIN Orders O
    ON O.CustomerId = C.CustomerId

RESULT:
join

SELECT C.Name 
FROM Customers C 
  INNER JOIN Orders O
    ON O.CustomerId = C.CustomerId

RESULT:
inner-join

JOIN and INNER JOIN Execution Plan Comparison

From the below execution plans comparison, we can see that both JOIN and INNER JOIN are producing the same plan and performance. Here I have used the Sql Server 2016 “Compare Execution Plans” feature to compare the execution plan produced by JOIN and INNER JOIN. This feature provides an option to highlight the similar operations and we can see that both JOIN and INNER JOIN is producing the similar operations and they are highlighted in the same color.


execution-plan-comparision

[ALSO READ] Compare Execution Plans in Sql Server 2016

JOIN and INNER JOIN produces the same performance counters

The below performance counters (i.e. execution plan properties) comparison shows that both JOIN and INNER JOIN produces the same performance result


execution-plan-properties-comparision

CONCLUSION

From the above various examples we can see that there is absolutely NO DIFFERENCE between JOIN and INNER JOIN. Even though both produces the same result and performance, I would prefer using INNER JOIN instead of just JOIN. As it is more readable and leaves no ambiguity. If we just write JOIN instead of INNER JOIN it is not obvious what it means or what the developer was intended while writing it. Whether the Junior Developer OR the developer moved from other Database technologies while writing JOIN, he would have thought it behaves as OUTER JOIN. Just avoid such confusions and to make it more readable and obvious I would prefer writing INNER JOIN instead of JOIN.

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